Conventionally, on a fixing roller, a fixing belt and the like in a fixing device, a release layer to prevent toner from adhering to the fixing roller or the like, and an elastic layer to adjust flexibility of the surface of the fixing roller or the like are formed.
The release layer and the like mainly use a resin as their material. However, a resin usually has a lower thermal conductivity than a metal or the like. Therefore, if temperature varies in the release layer or the like constituting the surface of the fixing roller or the like, it takes time to solve this unevenness. If toner is fixed in the state where temperature is varied in the circumferential direction or the axial direction of the fixing roller or the like, it causes uneven gloss and uneven color of the fixed toner.
The unevenness in temperature of the fixing roller or the like becomes conspicuous particularly if a heating member of the fixing roller or the like having a small heat capacity is used in order to cope with energy-saving. That is, if the heating member has a small heat capacity, for example, when a sheet of paper or the like passes through a nip part of the fixing roller or the like, the surface temperature of the fixing roller or the like is immediately lowered. However, since the release layer and the elastic layer have a low thermal conductivity and it takes time to raise their temperature, fixing is carried out without recovering the initial temperature. If this happens, temperature is consequently varied at the time of fixing. In this manner, if the temperature of the fixing roller or the like that is necessary for fixing toner is not recovered at the time of pressure contact and the roller surface has temperature unevenness, toner fixing capability is lowered. However, a predetermined heat capacity is necessary to maintain the fixing capability. Thus, it is difficult to realize both further reduction in heat capacity of the fixing member and reduction in temperature unevenness.